Glaucoma is an eye condition typically characterized by an increase in the intraocular pressure (IOP) of the eye to an abnormal level. A normal eye maintains a proper IOP by the circulation within the eye of aqueous humor. Aqueous humor is secreted from the ciliary body, passes through the pupil into the anterior chamber of the eyeball, and is filtered out of the eyeball via the trabeculum and the Canal of Schlemm (or Schlemm's Canal). With glaucoma, the aqueous humor excretory pathway is blocked, the aqueous humor cannot pass out of the eyeball at an adequate rate, the IOP rises, the eyeball becomes harder, and the optic nerve atrophies due to the pressure applied on its fibers leaving the retina. A characteristic optic neuropathy develops, resulting in progressive death of the ganglion cells in the retina, restriction of the visual field, and eventual blindness. Advanced stages of the disease are characterized also by significant pain.
Glaucoma treatment, if initiated early in the course of the disease, can prevent further deterioration and preserve most of the ocular functions. The goal of glaucoma treatment is to reduce the IOP to a level which is considered safe for a particular eye, but which is not so low as to cause ocular malfunction or retinal complications.
In the past, procedures and devices have been developed and implemented for providing an alternate route for aqueous humor to pass out of the eye. For example, in full thickness filtration surgery, a fistula is created through the limbal sclera, connecting directly the anterior chamber of the eyeball and the sub-conjunctival space. This provides an alternate route, allowing the aqueous humor to exit the anterior chamber of the eyeball through the fistula in the limbal sclera and to pass into the sub-conjunctival space. During healing, however, there is potential for cell growth and scar formation in the sclera and/or conjunctiva, potentially obstructing the fluid passage.
In guarded filtration surgery (trabeculectomy), a fistula created through the limbal sclera is protected by an overlying partial thickness sutured scleral flap. This procedure similarly provides an alternate route, allowing the aqueous humor to exit the anterior chamber of the eyeball, through the fistula in the limbal sclera, allowing the aqueous humor to pass under the scleral flap and into the sub-conjunctival space. Again there is a possibility of obstructing the fluid passage, due to the potential for cell growth and scar formation in the sclera and/or conjunctiva.
In a deep sclerectomy, a superficial flap is made in the sclera and then a second deep scleral flap is created and excised leaving a scleral reservoir or well under the first flap. A thin permeable membrane is exposed between the anterior chamber and the scleral reservoir. The procedure is non-penetrating in that no penetration is made into the anterior chamber. The aqueous humor percolates from the anterior chamber through the thin membrane into the scleral reservoir and into the Schlemm's Canal. This procedure can be difficult to perform and has not been shown to be fully effective in reducing IOP.
Trabeculoplasty procedures are procedures wherein a physician uses a laser to create holes in the trabecular meshwork in order to allow flow from the anterior chamber into the Schlemm's Canal. The two primary types of trabeculoplasty are argon laser trabeculoplasty (ALT) and selective laser trabeculoplasty (SLT). Trabeculoplasty may not be a suitable long-term treatment as the meshwork may close again, for example due to scarring.
The TRABECTOME® device of NeoMedix, Inc., has been proposed for another method for providing passage through the trabecular meshwork. The device is passed through a corneal incision and across the anterior chamber. The device's tip has a bipolar micro-electrocautery electrode that ablates and removes a strip of trabecular meshwork. As with trabeculoplasty, this procedure may not be a suitable long-term treatment as the meshwork may close again.
In addition to various procedures, drainage implant devices have also been developed and implemented. For example, some implants have a tube that is inserted through the limbal sclera. The tube provides an alternate route for the aqueous humor to leave the eye.
Many of these known devices and methods do not provide adequate regulation of IOP or have other potential drawbacks. For example, with some devices and methods, the initial procedure can cause excessive loss of aqueous humor from the eyeball during the early postoperative period, frequently leading to hypotony. With other devices and methods, there may be too much resistance to the flow of aqueous humor from the eyeball, thereby resulting in higher eventual IOP and an increased risk of late failure. There is also the risk that the drainage pathway will become clogged, for example due to iris prolapse or due to scarring, or that infection could occur because of the passageway into the eye. In certain valved implant devices, defects in and/or failure of the valve mechanisms can lead to either too much or too little aqueous humor exiting the eye. In procedures that drain into a “bleb” in the sub-conjunctival space, there is sometimes a risk of leakage or infection. Additionally, some implant insertion operations can be complicated, lengthy, and costly.
There continues to be a desire for improvements in treating glaucoma, to provide improved patient outcomes in an efficient manner.